1. Field of the Invention
The present invention relates to a stage apparatus including a movable stage supported to be movable in a specific plane, and a camera shake (image shake) correction apparatus incorporating the stage apparatus.
2. Description of the Related Art
As a first example of a camera shake correction apparatus (image shake correction apparatus/image stabilizer) of the related art, a camera, in which object images are captured by an image sensor (image pickup device/electronic device), is provided with a rear yoke (stationary support plate), a front yoke, a stage plate and a plurality of magnets. The rear yoke is fixed to an inner surface of the camera body, and the front yoke is positioned immediately in front of the rear yoke. The stage plate is positioned between the front yoke and the rear yoke, and is movable in a plane in a direction parallel to the both the front and rear yokes. The magnets are fixed to the rear surface of the front yoke. The image sensor and a plurality of coils are fixed to the front surface of the stage plate. The magnets, the front yoke and the rear yoke form magnetic fields, and the respective coils stay within these magnetic fields regardless of the positions thereof. One end of a flexible printed circuit (FPC) board is fixed to the rear surface of the stage plate. The one end of the FPC board is electrically connected to a coil, and the other end of the FPC board is electrically connected to a control circuit board (controller).
According to the first example of the related art, when the camera is shaken (for example, when an operator's hand unintentionally shakes), the controller passes an electric current through the coils. Each coil produces a driving force, whereby the stage plate and the image sensor slidably move. Thus the image shake of camera is corrected.
A second example of the related art is disclosed in Japanese unexamined patent publication No. 2011-81417.
According to this second example of the related art, a camera shake correction apparatus is provided with a stationary support plate fixed to an inner surface of a camera body, a stage plate, a plurality of yokes fixed to and projecting rearward from the rear surface of the stationary support plate, and a plurality of magnets fixed to the front of the respective yokes. The stage plate comprises a circuit board (a rigid material) and is slidably movable parallel to the stationary support plate.
The stage plate is provided, on the front surface thereof, with an image sensor that is rectangular in shape as viewed from the front, an X-direction drive coil on the right side (short side) of the rectangular-shaped image sensor, and a pair of Y-direction drive coils on the lower side (long side) thereof. The Y-direction drive coils are aligned in a l direction parallel to the long side of the rectangular-shaped image sensor and have the specifications (the same number of coil windings) as each other. Regardless of the position of the stage plate, the X-direction drive coil and the pair of Y-direction drive coils stay within the magnetic field formed by the rear part of yokes and the magnets.
According to the second example of the related art, when a controller inside the camera body passes an electric current through the X-direction drive coil, the X-direction drive coil produces a driving force in the X-axis direction (the direction parallel to the long side of the image sensor), whereby the stage plate moves linearly in the X-axis direction. When the controller passes the same amount of electric current through each of the pair of Y-direction drive coils, each of the Y-direction drive coils produces the same amount of driving force in the Y-axis direction (direction parallel to the short side of the image sensor), respectively, whereby the stage plate moves linearly in the Y-axis direction. On the other hand, when the controller passes two different values of electric current through the respective Y-direction drive coils, each of the pair of Y-direction drive coils produces a different value of driving force, whereby the stage plate rotates in an X-Y axis plane.
Upon detecting a camera shake, the controller supplies electric current to each drive coil for compensating (correcting) the image shake. For example, if the camera shakes in the X-axis direction, electric current is supplied to the X-direction drive coil, whereby the stage plate slides in the X-axis direction opposite to the direction of camera shake. Similarly, if the camera shakes in the Y-axis direction, the same amount of electric current is supplied to the pair of Y-direction drive coils, whereby the stage plate slides in the Y-axis direction opposite to the direction of camera shake. If the camera shakes in a rotational direction, the controller supplies electric current to the X-direction drive coil and to the pair of Y-direction drive coils, while each of the pair of Y-axis direction drive coils is supplied with a different value of electric current, accordingly, the stage plate rotates in the direction opposite to the rotational direction of camera shake.
These stage apparatuses and camera shake correction apparatuses are disclosed in Japanese Unexamined Patent Publication No. 2011-81417 and Japanese patent No. 4,385,756.
According to the first example of the related art, in general, the camera shake correction apparatus is provided with the control circuit board immediately at the rear of the rear yokes, and each of the coils (the stage plate) is electrically connected to the control circuit board via the FPC board.
However, in recent years, since cameras have become increasingly slimmer (i.e., camera body sizes have been increasingly reduced in the optical axis direction), there has also been an increasingly demand for a slimmer camera shake correction apparatus. However, since the control circuit board is positioned at the rear of the rear yokes, the thickness of the camera shake correction apparatus cannot be slimmed down.
According to the second example of the related art (Japanese unexamined patent publication No. 2011-81417), since there is only one X-direction drive coil, it is difficult to drive (move) the stage plate in the X-axis direction with a large driving force. This problem can be solved by providing a pair of X-direction drive coils in a direction parallel to the short side of image sensor on the stage plate so that the controller supplies the electric current at the same value to the pair of X-direction drive coils.
However, this solution (structure) still has the following problems.
If the pair of X-direction drive coils is positioned at the upper side and the lower side, respectively, of a reference straight line extending in the X-axis direction and passing through the center of gravity of an integrated movable body of the stage plate, the image sensor, the pair of X-direction drive coils and the pair of Y-direction drive coils, and if the distance in the Y-axis direction from the reference straight line to the each of X-direction drive coils is the same, the stage plate would move linearly in the X-axis direction upon supplying the same value of electric current to the pair of X-direction drive coils.
However, due to increasing demand for miniaturized and light-weight camera body, the size of stage plate has become smaller (miniaturized), thereby causing unwanted restrictions on the positioning of the image sensor, the pair of X-direction drive coils and the pair of Y-direction drive coils fixed to the stage plate, and hence the distance in the Y-axis direction from the reference straight line to the each of X-direction drive coils sometime need to be made to differ from each other. If the same amount of electric current is supplied to the each of X-direction drive coils having a different distance from the reference straight line, the stage plate does not move linearly but only rotates, and the camera shake correction either in the X-axis direction or the rotative direction cannot be carried out precisely.
Even in the case of each of the X-direction drive coils being positioned at different distances in the Y-axis direction from the reference straight line, the stage plate can move linearly in the X-axis direction if a different amount of electric current is supplied to the each of X-direction drive coils; however, the control of electric current supply to the pair of X-direction drive coils would become complicated. Additionally such a structure requires at least two independent drivers for driving the pair of X-direction drive coils, which would increase the number of component parts.
Linear movement of the stage plate in the X-axis direction can also be achieved by providing different types of X-direction drive coils (i.e., two coils having different coil windings). When the same amount of electric current is supplied to the pair of X-direction drive coils having different coil windings, each coil produces a different driving force in accordance with the respective number of coil windings, whereby the stage plate moves linearly in the X-axis direction. However, this structure requires at least two types of X-direction drive coils having different coil windings, which would result in the higher production cost.